1. Field of the Invention
The present invention relates to a transflective liquid crystal display device, and more particularly, to a transflective liquid crystal display device with balanced color purity in both transmissive and reflective modes.
2. Description of the Related Art
Liquid crystal display (LCD) devices are widely used for display devices, such as a portable televisions and notebook computers. Liquid crystal display devices are classified into two types. One is a transmission type liquid crystal display device using a backlight as a light source, and another is the reflective type liquid crystal display device using an external light source, such as sunlight or indoor lamp. It is difficult to decrease the weight, volume, and power consumption of the transmission type LCD due to the power requirements of the backlight component. The reflective type LCD has the advantage of not requiring a backlight component, but cannot operate without an external light source.
In order to overcome the drawbacks of these two types of LCDs, a transflective LCD device which can operate as both a reflective and transmission type LCD is disclosed in U.S. Pub. No. 2002/0003596. The transflective LCD device has a reflective electrode in a pixel region, wherein the reflective electrode has a transmissive portion. Thus, the transflective LCD device has lower power consumption than the conventional transmission type LCD device because a backlight component is not used when there is a bright external light. Further, in comparison with the reflective type LCD device, the transflective LCD device has the advantage of operating as a transmission type LCD device using backlight when no external light is available.
FIG. 1 is a sectional view of a conventional transflective LCD device, which helps to illustrate the operation of such devices. As shown in FIG. 1, the conventional transflective LCD device includes a lower substrate 100, an upper substrate 160 and an interposed liquid crystal layer 130. The upper substrate 160 has a common electrode 140 and a color filter 150 formed thereon. The lower substrate 100 has an insulating layer 110 and a reflective electrode 120 formed thereon, wherein the reflective electrode 120 has an opaque portion 122 and a transparent portion 124. The opaque portion 122 of the reflective electrode 120 can be an aluminum layer and the transparent portion 124 of the reflective electrode 120 can be an ITO (indium tin oxide) layer. The opaque portion 122 reflects the ambient light 170, while the transparent portion 124 transmits light 180 from a backlight device (not shown). Thus, the transflective LCD device is operable in both a reflective mode and a transmissive mode.
The conventional transflective LCD device, however, has a problem of different color reproduction levels (color purity) in reflective and transmissive modes, due to, referring to FIG. 1, the backlight 180 penetrating the transparent portion 124 through the color filter 150 once and the ambient light 170 reflected from the opaque portion 122 passes through the color filter 150 twice. This degrades the display quality of transflective LCDs greatly.